When it comes to telling locations: "At" is just a general word for saying something is somewhere. "In" is used for something that's in a 2D area or 3D space. The opposite of "in" is "out (of)". "On" is used for something that's on the outer surface of a 3D object. Usually it refers to the top of the object, but it may be the sides.The opposite of "on" is "off (of)". Ex. I am in the building = I am inside the building I am on the building = I am on the roof of the building. I am at the building = I am at the location of the building. I may be in it, on it or outside it. Ex. Clocks hang on walls and termites live in walls. We all live on this planet, except for people who live underground. They live in it. Sometimes it doesn't work as you'd expect. We generally use "in" for places that occupy an area like cities, countries, states, forests, deserts, oceans etc. It's much less obvious when the nouns are concepts. You just have to think abstractly. As for verbs, you have to memorise which verb uses what preposition. Sometimes you might be able to figure it out, but most of the time it's random.